To date, most chemicals such as propanal, propan-2-one, propan-1-ol and/or propan-2-ol, propylene, or isubutylene are derived from petrochemical sources. With diminishing global reserves of crude oil and increasing demand from developing countries, the pressure on oil supply and demand will grow and alternative bio-based chemicals are being developed. The current generation of biochemicals that use either food or non-food crops to produce sugar or cellulose-based feedstocks may have drawbacks relating to land-use, food-security, and volatility of supply and environmental issues.
Propan-2-one is an important solvent with an annual demand of 2 million metric tonns per annum in the United States. Propan-2-ol is used as solvent for coatings or for industrial processes with a capacity of 3 million metric tonns per annum. 1-propanol is important in production of drugs and cosmetics and is considered as fuel substitute. Isobutylene is a chemical building block and key precursor for numerous chemicals. The worldwide demand for isobutylene has been estimated to exceed 10 million metric tons per year and its market value at 25 billion US dollar.
It has long been recognised that catalytic processes may be used to convert gases consisting primarily of CO and/or CO and hydrogen (H2) into a variety of fuels and chemicals. However, micro-organisms may also be used to convert these gases into fuels and chemicals. These biological processes, although generally slower than chemical reactions, have several advantages over catalytic processes, including higher specificity, higher yields, lower energy costs and greater resistance to poisoning.
CO is a major free energy-rich by-product of the incomplete combustion of organic materials such as coal or oil and oil derived products. For example, the steel industry in Australia is reported to produce and release into the atmosphere over 500,000 tonnes of CO annually.
The ability of micro-organisms to grow on CO as their sole carbon source is a property of organisms that use the acetyl coenzyme A (acetyl CoA) biochemical pathway of autotrophic growth (also known as the Woods-Ljungdahl pathway). A large number of anaerobic organisms including carboxydotrophic, photosynthetic, methanogenic and acetogenic organisms have been shown to metabolize CO to various end products, namely CO2, H2, methane, n-butanol, acetate and ethanol. When using CO as the sole carbon source all such organisms produce at least two of these end products.
Some microorganisms such as Clostridium acetobutylicum or Clostridium beijerinckii are known to produce propan-2-one or propan-2-ol as major by-products during butanol fermentation (ABE or IBE fermentation) (George et al. 1983), while propan-1-ol is a byproduct of fermentations with yeast Saccharomyces cerevisiae (Hazelwood et al. 2008). However, all these organisms rely on sugar or starch based substrates. Acetogenic organisms such as the closely related microorganisms Clostridium autoethanogenum, C. ljungdahlii, and C. ragsdalei are able to grow chemoautotrophically on CO or CO2/H2 containing gases as sole energy and carbon source and synthesize products such as acetate, ethanol, butanol or 2,3-butanediol, but neither propan-2-one nor propan-2-ol (Munasinghe and Khanal 2010). Although propan-2-one to propan-2-ol reduction have been shown in acetogenic species, the underlying principle is unknown (Ramachandriya et al. 2011).
It is an object of the invention to provide a method of production of propanal, propan-2-one, propan-1-ol and/or propan-2-ol or their precursors.